The present disclosure relates to an avalanche photodiode configured for use as part of an image sensor, such as a charge-coupled device (CCD) image sensor or a complementary metal-oxide-semiconductor (CMOS) image sensor. The present disclosure further relates to use of low-doping profiles in reach-through avalanche photodiodes for reduction of the ionization ratio, k, such as to values of less than 0.02.
Photodiodes, in general, convert light to electricity. In some cases, light reaches and excites a p-n junction, which then generates voltage or current. Typically photodiodes are used in image sensors, such as active-pixel sensors that include an array of pixels containing photodiodes and amplifiers. Some photodiodes may be integrated into a charge-coupled device (CCD) image sensor to receive light photons and to indicate sensed pixels by producing electrical output. Other photodiodes are integrated in complementary metal-oxide-semiconductor (CMOS) image sensors.
CMOS and CCD image sensors may be used in night-vision goggles and other night-vision equipment. CMOS and CCD image sensors are generally preferred relative to other sensor technologies due to low cost. However, it is Applicant's understanding that the best commercially-available sensitivity for CMOS and CCD sensors is on the order of starlight illumination (e.g., 1 millilux), which may be too low to meet standards for some night-vision equipment. A need exists for an improvement in CMOS and CCD image sensor sensitivity, such as an order of magnitude improvement in sensitivity, for effective use of CMOS and CCD image sensors in some such night-vision equipment. It is contemplated that improvement of the sensitivity of CMOS and CCD sensors might be applied to digital still or video cameras.